Information recording materials having an information recording layer for recording information on a supporting base include pressure-sensitive recording materials, thermosensitive recording materials, photosensitive thermosensitive recording materials, photosensitive pressure-sensitive recording materials and inkjet recording materials. Such information recording materials, having the advantages of allowing the use of a relatively simple device, maintenance ease and the absence of noise emission, are extensively used in measuring and recording instruments, facsimile machines, printers, computer terminals, labeling devices, ticket vending machines and so forth.
In recent years, enhanced functions and performances of these information recording materials have come to be required, and to meet this requirement materials having a multi-layer coats consisting of two or more coats over a supporting base are now used. For instance, with a view to achieving superior color optical density, sensitivity and image stability together with a plurality of tints, information recording materials consisting of multiple coats have come into practical use, including ones in which one or more protective layers are disposed over the information recording layer, ones in which an undercoat is laid between the supporting base and the information recording layer, ones in which both a protective layer and an undercoat are provided, and one in which two or more information recording layers, instead of only one, are disposed.
In a conventional method of manufacturing information recording materials having multi-layer coats consisting of two or more coats over the supporting base, one coat is applied and dried at a time over the supporting base in a consecutive coating process, and the coating procedures used include air knife coating,. blade coating, rod coating and reverse roll coating. However, information recording materials manufactured by any such consecutive coating process are poor in. coat quality, involving such problems low productivity due to the large number of times of coating in addition to the infiltration of the upper coat liquid into the lower coat or coats, pin holes in the upper coat due to bursts during the application of the upper coat and unevenness in coat quality arising while coats are applied consecutively over a long time.
On the other hand, while in the field of photosensitive materials for photographic use simultaneous multi-layer coating processes, such as curtain coating and slide bead coating, in which multi-layer coats are formed by applying a plurality of coating liquids are applied at the same time, are employed. The reason for this practice is that coating liquids for photosensitive materials for photographic use contain gelatin as a binder, which can be gelled by cooling immediately after the coating liquid is applied over the supporting base. In this way, immobilization of the coating liquid by gelatin even enables the simultaneously applied multi-layer coats to be dried and fixed without allowing the layer configuration to be disturbed by inter-layer mixing.
However, the use of a simultaneous multi-layer coating process for the manufacture of thermosensitive recording materials, which are a type of information recording material not permitting the use of gelatin because of its thermal coloring property, involves a problem that it would invite inter-layer mixing between the layers of the multi-layer coats and cannot provide adequate performance as thermosensitive recording materials. Also, the use of a simultaneous multi-layer coating process for the manufacture of ink jet recording materials, which use no gelatin to secure the absorptiveness and absorbing velocity of ink, involves a problem that it would invite inter-layer mixing between the layers of the multi-layer coats and cannot provide adequate performance as ink jet recording materials.
Patent Document 1 proposes a manufacturing method for information recording materials which do not permit addition of gelatin to coating liquids, which prevents the occurrence of inter-layer mixing even if a curtain coating process, one of simultaneous multi-layer coating processes is used.
Patent Document 1 proposes to prevent inter-layer mixing by curtain-applying a plurality of coating liquid films with an intermediate coating liquid film being disposed between two coating liquid films to separate the films whose viscosity is increased when they come into contact or are mixed with each other. Patent Document 1 also proposes to prevent inter-layer mixing by utilizing the increase in viscosity over time resulting from the mutual contact or mixing of at least one pair of two adjacent layers constituting a multi-layered coating liquid film. And as a specific example of gradually increasing the viscosity over time when the two coating liquids are brought into contact or mixed with each other, a combination of emulsion of a polymer containing carboxyl groups, which react with alkali to be dissolved, with alkali is cited.
Or in ink jet recording materials which are obtained by coating polyethylene laminate paper with an ink-receptive layer, usually coating of 100 μm or greater wet thickness is required, and this involves a problem of taking a long time to dry and, on account of susceptibility to irregularities in coating due to uneven distribution of liquid during the drying, a lack of uniformity in the coating.
As a way to solve these problems, for instance Patent Document 2 proposes a method of manufacturing an ink jet recording material which uses a polymer material having a property to increase in viscosity at low temperature, and to dry this polymer after it is set by being caused to pass a cooling zone.
Patent Document 1: WO01/076884
Patent Document 2: Japanese Patent Application Laid-Open No. 2004-50785